Straying from topic slightly...actually, I wanted to make sure graphic novels or comics were even viewable before I bought the one featured in this thread. (And I wondered if it was my device specifically that was having a problem.)
With the troublesome $1.99 comic, I did the following:
From the Vox library shelf, long pressed the comic until a menu came up. Chose to remove the book from the library.
Went to the Kobo web page on my laptop, went into my account, looked at my purchase history, where the item was listed. It was not in my library. I clicked on "purchased", it was listed there. I selected the comic and bookmarked it. I then synced the library on the Vox and the comic downloaded again. It is in my library on the web page, and it is displaying properly now on the Vox, so it looks like a problem with the download.
As for the preview issue, maybe it's just not going to work with graphic novels.